This invention relates to an easily realizable, remotely adjustable length of an antenna element (monopole) in order to extend the operating frequency range.
The proper length of an antenna monopole (single antenna element) or dipole (two antenna elements or monopoles), or any other type of antenna consisting of more monopoles, for a given feeding point (radio frequency signal connection point) and antenna impedance, is inversely proportional to the operating frequency. Proper operation of the same antenna at different frequencies or frequency bands is achieved with the length of the antenna being variable and preferably remotely adjustable for the current operating frequency. If the required operating frequency band is wide, the antenna length has to vary in a wide range from very short to very long. There are also other important factors, which any long (few tens of feet) antenna, meant for outside free air operation, should fulfill: reliable mechanical and electrical operation in any position, weatherproof and lightweight construction, etc.
One of the solutions for continuously varying the length of an antenna may be based on a telescope principle. Antennas utilizing this type of mechanism are widely found in automobiles, where the telescope feature is used to erect or retract the antenna manually or remotely. Such an antenna would be too heavy for having tens of feet in maximum length, with a complicated and bulky length-adjusting high-power mechanism. Since the telescope antenna consists of several moving sections, there would always be a potential problem of having poor electrical contact between the sections; furthermore, there is an inherent problem with the telescope principle: the minimum length of the antenna cannot be less than the length of its longest section.
Using a metal tape as the actual antenna, extended from a power returnable metal tape mechanism, would be a better solution. Length variation is easily achieved by just pulling out or releasing back the metal tape with a thin insulating line in a strong, lightweight insulating tube.